Zinc glycerolate has been used in pharmaceutical preparations and as an additive used in plastics, rubber and resins to confer special properties.
Blewett et al in U.S. Pat. No. 3,859,236 describes the stabilisation of vinyl halide resin compositions with divalent metal propanetriolates, in particular, the stabilisation of vinylchloride polymers with a zinc compound. The zinc propanetriolate was prepared from zinc acetate and a large excess of glycerol by heating under nitrogen to 160° C. for 6 hours to give a yield of only 34% based on the zinc. Reaction at 220° C. gave quantitative yield. A similar reaction, using zinc carbonate at 200° C., afforded the product in 79% yield.
Taylor in United Kingdom Patent 2,101,132B (U.S. Pat. No. 4,544,761) describes a method for combining a zinc compound with propanetriol to afford a polymeric and plastic plate-like zinc propanetriolate. The method of preparation of this polymer comprised mixing zinc oxide, or a zinc oxide forming material, with propanetriol in the proportion of about fifty parts by weight of zinc-containing compound to approximately 500 parts by weight of propanetriol, raising the temperature to about 260° C. and maintaining that temperature under constant stirring until added zinc oxide was predominantly converted to the propanetriolate, with evolution of water. The reaction was claimed to proceed at lower temperatures more slowly. The zinc propanetriolate polymer had to be isolated from the large excess of glycerol by pouring the cooled mixture into water, filtering, washing and drying. The material has been shown to possess a layered structure by T. J. Hambly and M. R. Snow in Aust. J. Chem 36, 1249 (1983).
Taylor in U.S. Pat. No. 4,876,278 (PCT International Application WO 87/01281; AU86/00251; United Kingdom 2,191,941) describes pharmaceutical applications of zinc propanetriolate. He describes a method of applying the material through transdermal absorption. It is claimed to have fungicidal, antiarthritic, antimicrobial and bacteriostatic activity.
Taylor in Australian patent 584,238 (PCT International Application WO 87/01379; AU86.00249) describes a modification of rubber and plastics by addition of the zinc propanetriolate material prepared in a manner as described above in United Kingdom 2,101,132B during manufacture or processing, as well as controlling the addition and processing to selectively arrange the additive particles in the organic polymer, thereby improving either the tensile strength of the composite material or its resistance to deterioration by ultraviolet light.
In U.S. Pat. No. 4,544,761, Taylor claims that the reaction between ane excess of propanetriol and a zinc compound can occur at temperatures around 260° C. For example, propanetriol (5.4 mole) and zinc oxide (0.614 mole) were reacted together at 260° C. for 1 hour to afford a 90% yield of polymer. The reaction was also stated to be slow below a temperature of 210° C.
In U.S. Pat. No. 4,943,326, Taylor claims that crystalline zinc propanetriolate could be formed by subjecting a zinc oxide suspension in propanetriol to microwave irradiation. Although this technique involved a saving in time, the temperature for effective conversion was subsequently found to exceed 190° C. Again a large excess of glycerol was required.
Bos in U.S. Pat. No. 5,475,123 describes a method of manufacture of zinc glycerolate which involves reacting a divalent metal including zinc, a polyhydroxy compound and a catalyst such as zinc acetate.
Typically the zinc glycerolate of the prior art is made up of crystals of 1 to 100 micrometer and usually from 10 to 1000 micrometer. Pin milling or jet milling may be used to reduce the size to 1 to 20 microns.
When zinc glycerolate of 1 to 20 microns is used as a nucleating agent it is difficult to disperse and deagglomerate causing blocking of extruder screens and resulting in a plastic product of low clarity, high haze and physical properties less then desirable.